Solar heating type swimming pool covers have become a common addition to swimming pools in recent years as a cost efficient means for maintaining the temperature of the pool water at a comfortable level. The traditional forms of energy used in heating a pool are electricity and natural gas, but as these forms of energy become scarce and more expensive, the use of energy saving solar pool covers becomes more attractive.
These covers are usually fabricated of laminated plastic sheet material and may contain entrapped air chambers or bubbles for added flotation and heat retention. The main function of a solar cover is to prevent the loss of heat from the heated pool to the ambient atmosphere. The three modes by which heat is lost from an open body of water to the surrounding atmosphere are evaporation, surface convection, and surface conduction. By spreading a solar cover over the pool surface, the loss of heat by evaporation is essentially eliminated, while heat losses due to surface convection and conduction are substantially reduced. The construction of the cover is such that heat absorption from sunlight is increased.
The early pool covers were usually made of a single sheet of plastic, vinyl, or canvas. The advent of improved plastic technology and great interest in using solar radiation as an inexpensive source of energy has resulted in a number of improvements in the design and application of solar pool covers.
U.S. Pat. No. 4,103,368 to Locksaw, discloses a cover having a laminated structure of thin metal sheet sandwiched between transparent and opaque sheets of plastic. The cover is stored as a cylindrical wrap around a locus. Sleeves formed in the cover surface may be inflated to unfurl the wrapped cover. Spring fingers attached to the cover are biased to aid in transferring from the unwrapped (spread on the pool surface) to the wrapped configuration.
The problem of accumulation of rain water on plastic solar pool covers with inflatable air pockets is recognized in U.S. Pat. No. 4,313,421 Trihey, 1982. Trihey teaches the use of a two layer plastic cover having segmented air pockets spaced between downwardly projecting crests, wherein drainage holes are disposed to drain off excess rain water.
An alternative to the laminated sheet construction cover is disclosed in U.S. Pat. No. 4,470,404 to Kremen. A number of black plastic strips are submersibly suspended inside a pool which absorb solar radiation and transfers the collected energy to the pool by heat conduction.
As is the case for most solar pool covers, Trihey and Kremen provide for outside, exposed storage of their covers, by rolling them up about a drum or roller at one end of the pool.
The use of pulleys and cables applying balanced tension to extend or withdraw a cover over the entire pool surface is disclosed in patents such as U.S. Pat. Nos. 2,754,900 of Karbonick (1952), 3,019,450 of Karasiewicz (1962), and 3,864,761 of Stadler (1975). It is also old in the art to use light-weight rip-resistant materials for pool cover durability and safety; e.g., U.S. Pat. No. 3,593,757 of Haynes, 1971. Other inventions which are in the general field of related art but which do not anticipate the advantages of this invention include U.S. Pat. No. 2,845,976 which discloses a collapsible roll-up container and U.S. Pat. No. 4,512,332 which discloses a solar pond construction.
Despite all of these advances made in the field of solar pool covers, there are still problems that exist with exposure to all the seasonal elements during storage of the cover, including wind, rain, ice, snow and especially summer heat and sunlight. The pool covers are usually stored by being folded at pool side or rolled onto a special reeling device at one end of the pool. Particularly during the summer months, a large amount of heat builds up and is trapped within the folds or layers of the stored pool cover. Without the cooling effect of water a temperature of 125.degree. F. can be reached in a clear plastic roll having air space construction on a sunny day within two hours or so, even when ambient temperature is relatively cool. At this temperature the plastic warps and the pool cover loses shape. Furthermore, in any degree of sunlight, plastic will degrade over a period of time, especially if translucent. Consequently, the appearance and usefulness of the pool cover deteriorates with time, sometimes with alarming rapidity.
For these reasons, the manufacturer of solar pool covers unanimously recommend that stored solar pool covers be protected from the elements (sun, rain, snow, wind). However, according to present practice the generally makeshift procedure of draping a relatively heavy blanket over the rolled up cover is awkward and inconvenient, and therefore is frequently neglected by the swimmer who reels in the pool cover. He or she is generally more interested in swimming than in protecting the rolled-up solar cover, and is usually unaware of the rapidity with which heat can build up and/or the cumulative damage inflicted by even short but frequent exposures by the sun.
Further, upon reeling up the cover, some pool water is present on at least the underside of the cover, which water is trapped in the rolled-up cover. This water can turn to steam on hot days, which due to the added presence of chlorine chemicals can yellow and accelerate the degradation of the plastic.
Therefore, there is an urgent need for a protective blanket for solar pool covers whose method of use offers automatic retraction, easy manipulation, convenient storage and protection.